This invention relates to soluble amide-imide-ester polymeric compositions and resinous blends containing such compositions, to methods of preparing such compositions and to the solid resinous coatings that such compositions provide, particularly on metal electrical conductors such as copper wire.
Terephthalate and isophthalate polyester compositions have been widely accepted in insulating electrical conductors such as copper and aluminum wire and foil. The heat shock and solvent shock properties of these polyesters, including those employing tris(2-hydroxyethyl)isocyanurate as a polyol component, have been considered one of their main weaknesses. Some manufacturers employ linear polyester overcoats in efforts to upgrade the heat and solvent shock. While some of these polyester compositions have acceptable thermal properties for most uses, applications which require higher, more reliable thermal life are increasing.
Aromatic polyimide compositions, primarily those derived from aromatic dianhydrides and primary aromatic diamines are employed as coatings where continuous reliable operation at temperatures in the 200.degree.-220.degree. C. range is required. These compositions are derived from aromatic polyamic acid precursors that are prepared in and are soluble in expensive solvent systems. The imidization occurs after these precursors have been applied to the conductor and the condensation (splitting out a mole of water per mole of imide groups formed) has a tendency to produce blistered coatings.
Polyester-imide compositions have been made in an effort to strike a balance between the properties of the foregoing polyesters and polyimides. In general, the compositions that have substantial imide content must employ expensive solvents and are characterized by a substantial number of disadvantages of the polyimides. The compositions that are soluble in inexpensive solvent systems have a low imide content and are thus very close to the polyester compositions in properties.